1. Field of the Invention
The present invention relates to a crystalline silica particulate material and a production process for the same, as well as to a crystalline silica particulate material-containing slurry composition and a crystalline silica particulate material-containing resinous material.
2. Description of the Related Art
As a method of turning amorphous silica into crystalline silica by crystallizing the amorphous silica, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 61-58822, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 63-233008, and Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2001-003034 disclose commonly-known methods in which a considerable amount of an alkali metal or alkaline-earth metal component is added to amorphous silica and then the resulting mixture is heated. These methods have brought about purposes to which the produced crystalline silica cannot be applied as a raw material, because they are adversely affected by the alkali metal or alkaline-earth metal component that has been left in the produced crystalline silica in a large amount.
Moreover, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2-022119, and Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2002-154818 disclose the following commonly-known methods, respectively: a method of adding alkali metal fluoride to amorphous silica; and a method of adding halogenated aluminum or halogenated calcium to amorphous silica. However, the use of halogen makes the cause for environmental pollutions, leading likewise to posing the problem of limited purposes.
In addition, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 5-193926 discloses another commonly-known method in which amorphous silica particles enclosing cristobalite particles in the interior are subjected to a heating treatment. However, the method is low in the productivity, because it necessitates two extra steps, namely, an extra step of preliminarily producing cristobalile particles each making a seed crystal, and the other extra step of synthesizing amorphous silica so as to enclose the resultant cristobalite particles.
Moreover, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2008-162849 discloses commonly-known high-purity cristobalite particles in which a metal selected from the group consisting of aluminum (Al), magnesium (Mg) and titanium (Ti), and/or an oxide of the same, exists in an amount of from 200 to 2,000 ppm by metallic conversion on some of the surface or on the entire surface. A method for producing the high-purity cristobalite particles, however, has left room for improvement, because it is adversely affected by a large addition amount of the metals required, and by a large remaining amount of metallic impurities.